This invention relates to a method of manufacturing a cooperating threaded lead screw and sleeve mechanism, such as for use in a linear actuator, using a hydroforming process.
A linear actuator is a well known device that is adapted to effect linear movement, typically reciprocating linear movement, of a workpiece along a desired path of movement. A typical linear actuator includes an electric motor having a rotatable output shaft that is connected through a gear train to a lead screw and nut mechanism. When the electric motor is actuated, rotation of the output shaft causes corresponding rotation of the lead screw. The lead screw is typically formed from an elongated shaft having an external helical thread provided on the outer surface thereof. The nut is typically formed from a block of material having an opening formed therethrough, with an internal helical thread formed on the inner surface thereof. The nut is mounted on the lead screw in such a manner as to be restrained from rotating with the lead screw when the electric motor is actuated. The helical threads of the lead screw and the nut cooperate with one another such that rotation of the lead screw causes linear movement of the nut axially along the lead screw. The direction of such axial movement of the nut (and of the workpiece connected thereto) is dependent upon the direction of rotation of the lead screw.
A variety of methods are known for forming lead screw and nut mechanisms of the general type described above. Typically, the lead screw and the nut are each formed from solid pieces of material to desired rough shapes, then machined to precise final desired shapes. Although known methods have been effective, it would be desirable to provide an improved method for manufacturing same.
This invention relates to a method of manufacturing a externally threaded screw and internally threaded sleeve mechanism without the use of machines by using a hydroforming process. Initially, an inner sleeve, an intermediate sleeve, and an outer sleeve are disposed concentrically within one another. The inner and outer sleeves are preferably formed from a rigid metallic material, while the intermediate sleeve may be formed from any desirable spacer material. The concentric sleeve assembly is then disposed within die halves of a hydroforming apparatus and hydraulically expanded such that an external thread is formed on the inner sleeve and an internal thread is formed on the outer sleeve. The intermediate sleeve is then removed in any desired manner, such as by melting or chemical dissolution. The relatively small space remaining between the inner and outer sleeves allow for relative rotation therebetween. Alternatively, the inner and outer sleeves can be hydroformed in separate operations for subsequent use.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.